The present invention refers to an automatic safety syringe.
As is known, a syringe generally comprises a cylindrical body open at the rear to accommodate a plunger. A needle, hollow on the inside, is mounted a head end of the syringe body. By retracting the plunger the liquid contained in a vial is drawn into the syringe body through the needle. By pressing on the plunger the liquid contained inside the syringe body is injected, by means of the needle, into the patient""s body.
To comply with safety regulations and to avoid the transmission of infectious diseases, syringes must generally be used just once and then discarded. For this reason there is growing demand on the market for disposable syringes able to prevent further use thereof.
Moreover, syringes generally present drawbacks from the point of view of safety. In fact, once the syringe has been used, the needle remains exposed at the head of the syringe body, with the risk of accidental injuries or needle sticks.
This drawback is overcome in part by European patent EP 0636381 which describes a protective device for syringe needles. In this case, when the plunger of the syringe reaches the end of its stroke, the fore end of the plunger shaft catches the needle. When the injection is completed the user must manually retract the shaft; in this manner the needle is pulled by the head of the shaft into a safety position inside the syringe body which avoids accidental needle sticks.
Said solution has problems during hooking of the needle carrier and has the drawback that the user, having completed the injection, can forget to carry out retraction of the shaft, leaving the needle exposed and thus rendering the protective device ineffective.
Patent application PCT WO 99/37345 describes a disposable safety syringe which provides a needle-covering sleeve axially mounted on the syringe body and sliding from a retracted position, in which it leaves the needle exposed to allow injection, to a forward position in which it completely covers the needle, preventing re-use of the syringe and acting as a protection against accidental needle sticks.
Once the injection has been completed, the sleeve is automatically carried in the safety forward position, by means of an automatic system and without any operating by the user. However, such a solution presents some problems for the provision and driving of an additional member, such as a needle-covering sleeve.
The object of the present invention is to eliminate the drawbacks of the prior art, providing a disposable safety syringe that is practical, versatile, cheap and simple to make.
Another object of the present invention is to provide such an automatic safety syringe that is able to prevent further attempts at use.
Yet another object of the present invention is to provide such an automatic syringe that is extremely safe and able to prevent accidental injuries or tampering after use thereof.
These objects are achieved in accordance with the invention with the characteristics listed in appended independent claim 1.
Advantageous embodiments of the invention are apparent from the dependent claims.
The disposable syringe according to the invention comprises a syringe body hollow on the inside and open at the front and rear, a plunger that can slide inside the syringe body so as to be movable from a retracted syringe-filling position to a forward syringe-emptying position, and an injection needle integral with a needle-carrier that can be engaged at the fore end of the syringe body. The plunger is provided at the rear with a shaft that can be operated manually and brought out of the syringe body through the rear end thereof. The syringe comprises an injection needle integral with a needle carrier that can be engaged directly or by means of a supporting body at the fore end of the syringe body.
A hooking device is provided such as to hook the needle carrier in order to pull it into the syringe body, when the plunger reaches the end of its stroke after the injection has been carried out.
Furthermore an automatic device is provided which allows the shaft of the piston to be retracted into a retracted position after the injection has been carried out and after the hooking device has hooked the needle.
The peculiarity of the invention lies in the fact that locking means operationally connected to the shaft of the plunger are provided to block forward movement of the shaft when it is in the retracted position, after the injection has been carried out and the automatic shaft retracting device has come into operation.
The advantages of the disposable syringe according to the invention are evident. In fact, once the injection has been completed, the hooking device intervenes to hook the needle carrier, the automatic device to cause retraction of the shaft which pulls the needle inside the syringe body and the locking device to block any attempt, voluntary or involuntary, to advance the plunger shaft, which would cause the needle to re-emerge from the head of the syringe body.
In this manner the needle always remains protected inside the syringe body, avoiding the risk of accidental needle sticks and the possibility of re-use of the syringe.